Internal combustion engines, particularly in engines of the two-stroke type



May 2, 1967 R. L. JEAN-BAPT|STE sANMoRl 3,316,889

INTERNAL COMBUSTION ENGINES, PARTICULARLY IN ENGINES OF THE TWO-STROKE TYPE I Filed Sept. 14, 1964 3 Sheets-Sheet 1 rfy May 2, 1967 R. L. JEAN-BAPTISTE sANMoRl 3,316,889

INTERNAL COMBUSTION ENGINES, PR'I'LICULJHILIY` IN ENGINES OF THE TWO-STROKE TYPE Filed Sept. 14, 1964 mm. N#

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May 2, 1967 R. L. JEAN-BAPTISTE sANMoRl 3,316,889

INTERNAL COMBUSTION ENGINES, PARTICULARLY IN ENGINES OF THE TWO-STROKE TYPE Filed Sept. 14, 1964 3 Sheets-Sheet 5 United States Patent O1 3 316 889 INTERNAL COMBUSzIIOlN ENGINES, PARTICU- rIQPRJY IN ENGINES F THE TWO-STROKE 4 5 Claims. (Cl. 12S- 51) The present invention relates generally to internal combustion engines and has more particular reference to a new or improved internal combustion engine comprising `reciprocating pistons capable of withstanding high rotational speeds and of producing large specific powers.

A primary object of the invention is to provide an internal combustion engine comprising at least a group of cylinders made up of a pair of parallel cylinders arranged o-n the opposite sides of a crankshaft the major axis of which is normal to the plane containing the axes of the two cylinders, each cylinder containing a pair of oppositely mounted reciprocating pistons so as to be movable synchronously in opposite directions, the pistons associated with said cylinders being connected pairwise and diagonally by elements providing between them a direct connection which does not extend through the crankshaft one crankpin of which is, however, engaged by at least one element of said connection.

`Owing to this novel arrangement, there is no need for the crankshaft to take, as in known engines, the total thrusts resulting from the explosions or combustions in the cylinders, also from the inertia strains of the parts in motion, whereby the action exerted upon it is limited to the kinetic difference between such stresses although each crankpin directly takes the thrust due to the explosion or prevailing combustion.

Another object of the invention is to provide an internal combustion engine as aforesaid wherein the diagonally arranged pistons of the two associated cylinders belonging to a group are interconnected by an assembly made up of links hi-nged to the pistons, rockers and pitmans engaging a crankpin of the crankshaft, a direct connection being provided between the pitmans.

If desired, the two pitmans may be united to form a single member having a central recess surrounding the crankpin of the crankshaft, means being provided for taking care of the necessary transverse motion during the operating cycle.

Yet another object of the invention is to provide an internal combustion engine as aforesaid wherein the crankshaft comprises for each pair of cylinders two crankpins arranged adjacent -to each other but offset by 180. An axial passage may be formed in the crankshaft and may be connected by radial channels with roller bearings encompassing the crankpins so as to provide pressure lubrication by centrifugal action.

A further object of the invention is to provide an internal combustion engine as aforesaid wherein the pistons are provided with a tail extension in which is engaged the associated link comprised in said diagonal connection, hinging of the link to the rocker being advantageously performed by oscillating elements so as to obviate side reactions upon the piston.

The hinge axis of the rocker may be provided in an eccentered ring whose adjustment permits the distance between the axes of the rockers and consequently the compression rate of theengine to be modified.

Yet a further object of the invention is to provide a two-stroke engine having the aforesaid construction and wherein the tail extension of each piston is associated with an annular valve so encompassing said tail exten'- ICC sion as to ensure a frictional drive, said valve cooperat- .ing with a seat surrounding a port communicating with an inlet pipe for the combustion gases, said port being brought into communication, as the valve is frictionally lifted on the piston tail, with an enclosure defined between the rear face of the piston top and a cylinder head, transfer ports being, provided in the hea-d wall for ensuring transfer of the combustion gases from said enclosure to that part of the cylinder situated in front of the piston when the latter is moved toward its lower dead centre.

A still further object of the invention is to provide an internal combustion engine as set forth in the foregoing wherein said transfer ports are inclined with respect to the cylinder axis and are located substantially opposite to exhaust ports with respect to a cylinder diameter, particularly in the case of a supersquare engine so as to provide a transverse equiflow scavenging action along a dense and compact gas stream, the jets of transferred gases which correspond with the two oppositely mounted pistons of a cylinder being merged and clustered before moving in the same direction.

The arrangement comprising parallel and interconnected pairs of cylinders arranged on the opposite sides of a crankshaft permits the provision of groups of two cylinders capable of being assembled in suitable number so as to build an engine having the required number of cylinders. Each group may include an initially independent crankshaft, each crankshaft being then optionally provided at one end with a fluted or contoured tip so engageable as to perform the desired kinetic connection with a socket which is likewise uted or contoured and is provided in the end of the adjacent crankshaft..

With these and such other objects in view as will incidentally appear hereafter, the invention comprises the novel construction and combination of parts that will now be described by way of non-limitative embodiment with reference to the accompanying drawings forming a part of this disclosure and wherein:

FIGURE 1 is a plan view partly broken away of `a `suitable constructional form of the engine according to the invention.

FIGURE 2 is a corresponding elevational view also broken away.

FIGURE 3 is a sectional View along a plane at right angles to that of FIG. 2.

FIGURE 4 is a partial view showing a constructional modification.

FIGURE 5 is a part sectional View of the valve.

The internal combustion engine shown in the drawings is a four cylinder engine of the supersquare type operating on the two-stroke principle.

' This engine comprises a casing designated generally by 1 containing two associated groups each one being made up of two cylinders. As said groups are similar, only one group is described hereafter.

The group being considered includes parallel cylinders 2, 3 extending on the opposite sides of a crankshaft 4, each cylinder constituting one-half of the crankshaft casing.

Each cylinder contains two pistons 5 performing synchronous reciprocatory oppositely directed motions. In the upper dead centre position shown in the right hand side portion of FIG. 2, these pistons nearly come into contact. Each piston is formed in its top portion with a hemispherical chamber 6.

According to the invention, each cylinder piston is directly associated with the diagonally opposite piston of the associated parallel cylinder belonging to the same group so as to provide a rigid connection. This connection is performed by means of links 7, rockers 8 and pitmans 9, the rockers being pivotally supported by axes 10 through the medium of roller bearings 39.

Each diagonal connecting system for the pistons is secured to one of the crankpins 11 of the crankshaft 4 which are offset at 180 to each other so as to cause the thrusts exerted by each pair of pistons upon said crankshaft to be simultaneous, symmetrical and double acting.

The crankshaft 4 which is relatively very short is provided for each group of cylinders with two slightly spaced crankpins so that it behaves more or less like a camshaft. Its outline may be such that is geometrical projection defines a straight cylindrical volume. The small space between the crankpins is clearly visible in the showing of FIG. 3. Actually the pitmans 9 are mounted upon needle roller bearings 12 and the straight cylindrical outline of the crankshaft when considered in geometrical projection permits said bearings 12 and the big heads of the pitmans to be positioned from one end of the engine, proper keeping in position being performed by web plates 13 held by grub screws 14. Such plates 13 may also behave as balancing weights for the crankshaft.

Through the crankshaft 4 extends a channel 15 for pressure lubrication which communicates with the bearings 12 through thin radial channels 16. The oil in the channel 15 is directly forced with an impetus through the bearings 12 by centrifugal action so that adequate lubrication of said bearings is ensured depending upon the then prevailing running conditions of the engine without any need for a high pressure circuit. The channel 15 may be oil fed through a duct 17 from a pump such for example as a centrifugal pump.

In the constructional form shown in FIGS. 1 to 3, each pitman 9 has an open head 18 which surrounds the outer ring 19 of the associated roller bearing over slightly less than 180, the heads of the two pitmans associated with the same pitman being held in position by a ring20 adapted to their shape and axially retained by one of the web plates 13. Such an assembly permits a slight relative displacement of the pitmans by a rocking action about the roller bearing 12.

A constructional modification corresponding to this portion of the internal combustion engine is represented in FIG. 4. In this case, there is provided for interconnecting the two diagonally opposed pistons 3, one pitman 21 formed with a recess 22 having a box-like outline. This recess contains a whorl 23 adapted around the roller bearing 12 carried by the crankpin 11. The whorl 23 is separated from the opposite faces of the recess 22 in the pitman 21 by needle shoes 24 the stroke of lwhich is limited by associated abutments 25.

In the engine as shown, each pitman 9 (or the pitman 21) is `connected with the associated rocker 8 by the open big end 26 of a pitman which is inserted into the yoke 27 of the rocker. A needle roller bearing 29 is interposed between the big end of the pitman and the rocker raxis 30. This bearing is incomplete and the empty space is filled by a ring section 31 held in place by a cotte; pin 32. The yoke 26 of each rocker is closed on its two faces by portions of the yoke 27 of rocker 8, the needle rollers ofthe bearing 29 having a maximum length as clearly visible in FIG. 3.

An equivalent hinge system may be provided between each rocker S and the associated link 7. However, in the constructional form as shown, the link 7 is lfulcrumed by a narrow curved surface similar to a roller sector having its axis at C along a small reinforcing plate 34 for the piston upon which said surface may freely rotate. The end portion of the link 7 opposite to the piston 5 is concave and caps with interposed needle rollers 35 the ball-shaped head of the rocker 8. A minute axis 36 integral with the tail of the piston and entirely engaged therethrough is fulcrumed by a semi-circular portion 37 Ywhich is journalled in the head of the rocker 8 so as to retract the piston.

According to a feature -of the invention, the axes of the rockers are pivotally supported by bosses 4Gb formed is separated from the opposite faces bosses 40b formed on the casing by means of a pair of rings 40. The inner and outer bores of said rings are very slightly eccentered so that the possibility is afforded, owing to an angular adjusting motion of said rings, to modify the distance between the axes of the rockers belonging to the same cylinder and consequently the length of the articulated system and the compression rate of the engine. In order to make this adjustment possible, the rings are pinned to the axes (as shown) and the four axes may be interconnected outside by suitable means permitting (either manually or automatically e.g. by depression) a concomitant adjustment of the compression rate to be achieved.

The intake device for the two-stroke engine as shown will now be described. In this case, the suction of the combustion gases through the carburetor (or 4any other feeding unit) takes place at the same time as the compression. There is shown in the drawing at 41 the inlet ports for the engine and at 42 its exhaust ports.

According to the invention, the combustion gases lare fed through a closed enclosure defined behind each piston before penetrating into the corresponding cylinder. As shown, said enclosure is defined between the lower or rear face of the head of each piston 3 and the cylinder head 43. The last-mentioned head carries a guide 44 in which is slidably engaged the piston tail 46, thereby performing the required guiding action while permitting the usual skirt to be omitted. The piston tail 46 is surrounded by a tulip-shaped valve 47 made -of a very light metal sheet and engaged upon said tail 46 with a certain amount of friction so as to be frictionally driven owing to the elasticity of the collar 48 (FIG. 5). A circular trim 48h limits the opening stroke of the valve owing to the provision of the sleeve 41h and its inner rim. The inlet port 41 ends in a zone which surrounds the hinge between the link 7 and the rocker 8 while providing a seat 49 for the valve. The gases flow between the seat 49 and the piston guide which is connected with the cylinder head by partitions 60.

It will be seen that, owing to this arrangement, the valve provides a large flow section owing to its annular shape and contour. It is driven in both directions (upwards and downwards) owing to its friction along the piston tail, thereby `creating a satisfactory positive control.

The particular arrangement of the hinge and valve permits, owing to the location of the link 7 in the tail 46 of the piston 5, side reactions of the piston to be eliminated, the link 7 being constantly parallel with the cylinder axis. This completely eliminates those major frictional stresses which take place in `conventional engines.

It will be understood that an intake device of the aforesaid type is associated with each piston. The cylinders are provided in their walls with transfer ports 51 and exhaust ports 52. As shown in FIG. 2, the transfer ports are inclined so as to facilitate scavenging of the gases as described hereafter. Such ports begin to be uncovered at the outset of the piston stroke towards its lower dead centre.

The left hand side portion of FIGS. 1 and 2 contains arrows which show the way in which the scavenging action .takes place in the engine according to the invention. This scavenging method takes advantage `of the symmetry of the assembly. The inclined transfer ports provide in each cylinder two masses of fresh combustion gases which fiow as shown by the arrows while being closely associated to ensure the evacuation of burnt gases through the exhaust ports 52 toward the pipes 42. It will be seen that the scavenging action is of the transverse equiflow type on account of the very short stroke of the pistons by comparison with the size of the cylinder bore.

Spark plugs V53 provide proper ignition of the compressed gases at the correct time.

The pistons mounted pairwise in the cylinders may be fitted with ordinary rings but are advantageously fitted in the present construction with a particular type of rings involving a thermostatic control. Due to the elimination of the piston skirts, ya satisfactory side sealing action of the pistons should be achieved for the control of the distribution ports. Now in the present engine only the `exhaust ports need being closed oif at all times and as they are situated on one and the same side of the cylinder, it is suitable to apply the cold piston (i.e. the piston capable of providing a substantial clearance) against the corresponding side of the cylinder wall. This technical problem may be solved by the absence of inclined stresses along varying directions and also by the absence of side reactive stresses. Such an advantage results from the particular method of guiding the links.

According to the invention, there are provided one or two piston rings of usual shape the gap of which is directed toward the exhaust. On the transfer side a two-blade spring 55 is received in the ring-receiving groove between the latter and the ring itself 56 so as to provide an expansion which applies the piston and the ring against the opposite sides of the cylinder. Due to the fact that such an action is only necessary when the engine is cold, it may be omitted when it is hot. Such a result is obtained `owing to the very nature of the two-blade spring whose outer blade has an expansion coefficient larger than that of the inner blade, thereby creating a tendency for an expansion of the ring when in the cold state and a retraction of the two-blade spring in the ring-receiving groove when the piston is hot.

Another feature of the invention resides as described in the foregoing in the possibility of grouping or clustering elementary cylinder blocks comprising one or two groups of pistons so as to build an engine comprising a larger number of cylinders. This is rendered possible by the compact structure of the engine, its perfect balance, -its high cyclic evenness coupled with adequate symmetry of the stresses, the small size of the crankshaft and the overall valve distribution. The possibility is even afforded, if desired, to provide elementary cylinder blocks that have beenl regulated on the testing bench and subsequently assembled vwhereby engines having four, six, eight or twelve cylinders can be built.

There `is no showing in the drawing of the method of assembling cylinder casings as this may be done in any suitable way depending upon requirements. In order to permit the assembly, each crankshaft may carry at one -end a uted boss 57 adapted to cooperate with a companion uted socket 58 provided at the other end of the adjacent crankshaft, thereby ensuring adequate kinetic connection between the crankshaft units.

The operation of the engine will now be described while omitting those explanations which are common knowledge in the art of operating two-stroke internal combustion engines, only those particular features which are` related with the invention being set forth.

While in known engines having reciprocating pistons, the several forces applied to the pistons and to the pitmans or connecting rods are directly and entirely transmitted to the crankshaft which performs a connection and compensation of said forces so as to provide a resultant equal to the algebraic sum of the motive thrusts and inertia stresses, the latter being very large when the engine rotates at a high speed, the crankshaft only takes, in the construction according to the invention, the differential strain between said stresses owing to the rigid connection which exists between the two diagonally arranged pistons belonging to the two cylinders of the same group. Actually when the right hand side pistons in FIG. 2 are for example at their upper dead centre position, the left hand side pistons are at their lower dead centre position so that, owing to the direct rigid connection between the diagonally arranged pistons, the explosion which is going to take place on the right hand side directly absorbs not only the inertia of the pistons and corresponding couplings but also that of the pistons moving in the opposite cylinder. Starting from a particular running speed, the sum of the parasitic forces tends to reach and then to exceed the explosion thrust which amounts to say that the crankshaft is relieved from an enormous strain as takes place Iwithout any mechanical benefit in conventional engines. It is only this considerable reduction of the stresses and strains which permits high speeds to be reached with proper safety conditions.

The attainment of very high speeds of rotation is also rendered possible due to the use of positively controlled intake valves of the above-stated type. It will be seen from an examination of FIG. 2 that as the piston moves olf the lower dead centre position, it upwardly drives with it, owing to the friction exerted upon the tail 46, the valve 4'7. thereby permitting the intake of gases drawn from the carburetor through the pipes 41. These gases then reach the spaces defined between the pistons 5 and the cylinder head 44. The inflow of fresh combustion gases immediately under the piston eflicaciously cools the latter while staving off the provision of an additional heater.

As soon as the valve 47 has reached the end of its upward motion, its edge comes into abutting position whereupon the piston continues to move alone. When the piston moves down, it immediately drives with it the valve due to the aforesaid friction, thereby closing the same. This downward motion of the valve is facilitated by the precompression pressure generated in the aforesaid space.

It will be seen that owing to the much longer stroke available for the piston, the control of the` valve is performed under perfectly safe conditions devoid of misadjustment risk. The valve is powerfully braked and held `upon the associated seats in each of its arrested positions owing to the prevailing friction and pressures the action of which largely exceeds the inertia resulting from the mass of the valve itself. Vibrations and olting motions of conventional systems are thus avoided, also overrunning of the valves, whereby proper intake and exhaust are always maintained irrespective of the rotational speed of the engine.

The method of achieving a transverse equiow savenging action has been described in the foregoing. In a twostroke internal combustion engine, the object of this is to accumulate as swiftly and completely as possible the fresh 'combustion gases at one end of the cylinder thereby providing what may be termed a compact buffer for driving out burnt gases.

In the engine of the type under consideration, in which `the cylinder bore is much larger than the piston stroke, it

is possible to conceive that the cylinder ends are located along the diameter and not heightwise. According to the invention, the two sets of inclined transfer ports permit the mass of fresh combustion gases to converge toward the bottom end of the double cylinder opposed to the exhaust ports and then to flow back toward the latter while driving out the burnt gases. Moreover the transfer ports are advantageously so disposed as to cause the accumulation of fresh combustion gases at one end of the cylinder to take place from four points that are arranged diagonally pairwise. Such a grouping permits a dense scavenging front or buffer to be obtained, the losses of fresh combustion gases to be minimized and a better accumulation of such fresh gases as come from the spaces under the pistons to be achieved.

Minor constructional details may be modified without departing from the scope of the subjoined claims.

What is claimed is:

1. An oversquare internal combustion engine comprising at least a group of cylinders made up of two cylinders having a large diameter bore and a middle transverse plane, the axes of said cylinders being arranged in a single plane, a crankshaft having two crankpins and extending normally to the plane containing the axes of the two cylinders and between said cylinders, a first and a second reciprocating piston mounted in opposition in each cylinder for synchronously moving in opposite directions, a rocker connected to each piston, a roller sector cooperating with said rocker and having an outer diameter and an inner diameter, a plate member provided on said piston, said outer diameter of said sector rolling on said plate member, while said inner diameter is journalled on said rocker, a bearing semi-circle provided in said rocker, a pin carried by said piston, said pin being laterally slidable on said bearing semi-ci-rcle, a pitman directly connecting the first piston rocker of one cylinder to the diagonally opposed second piston `rocker of the other cylinder, means on said pitman for engaging one crankpin of said crankshaft, intake means provided in each cylinder near one end of a diameter `contained in said middle transverse plane of said cylinder, and exhaust means provided in said cylinder near the other end of said diameter, so as to ensure within said cylinder a scavenging action 'by transversely directed equicurrents about said middle plane.

2. An internal combustion engine according to claim 1, comprising a box-shaped central recess provided in said pitman, a whorl member surrounding said `crankpin of the crankshaft, said whorl member being transversely shiftable through said recess, and ball-bearing means located between said whorl member and said recess.

3. An oversquare internal combustion engine comprising at leas-t a group of cylinders made up of two cylinders -having large diameter bore and a middle transverse plane, the axes `of said cylinders being arranged in a single plane, :a crankshaft having two crankpins and extending normally to the plane containing the axes of the two cylinders and between said cylinders, a rst and a second reciprocating piston mounted in opposition in each cylinder for .synchronously moving in opposite directions, elements directly connecting the tir-st piston of one cylinder to the diagonally opposed second piston 'of the other cylinder, means on said elements engaging `one crankpin of said crankshaft, intake means provided in each cylinder near Ione end of a Idiameter arranged in said middle transverse plane of said cylinder, exhaust means provided in said cylinder near lthe other end of said diameter, so as to ensure within said cylinder a scavenging action by transversally directed equicurrents about said middle plane, a preoompression chamber arranged behind each piston, an intake valve for admitting fresh gases into said precompression chamber, said intake means commun-icating with said precompression chamber for admitting said fresh gases into said cylinder near said end of said diameter, a tail portion rigid with each piston, arranged in said precompression chamber, a flared seat surrounding said tail portion, provided at the bottom of said precompression chamber, intake openings provided in said seat, and a flared intake valve surrounding said tail portion so as to ensure `a positive anti-adjustment drive by a friction action, said valve cooperating with said seat by its llared profile contacting said ared seat, said valve being made of thin-gauge light material for easily moving with said piston tail portion.

4. In an internal combustion engine comprising at least two cylinders whose axes are parallel and disposed in a single plane, a crankshaft having a plurality of crankpins and disposed perpendicular to said plane and between said cylinders, a pair of reciprocating pis-tons mounted in opposition in each of said cylinders for synchron-ously moving in 4opposite directions, and means connecting one piston of one cylinder to the diagonally opposed piston of the `other cylinder and to said crankpins of said crankshaft; the improvement comprising intake passages for the transfer of gas from a compression zone at the rear of the piston to a combustion zone between the pistons of each cylinder, said transfer passages terminating in the combusion zone adjacent and being inclined toward one end of a diametral line that lies on the middle transverse plane of the cylinder, said transfer pas-sages being dispose-d symmetrically on opposite sides of said middle transverse plane, and exhaust ports symmetrically disposed on opposite sides of said middle transverse plane adjacent the other end of said diametral line, the engine being of lthe oversquare type in which the stroke of the pistons is substantially less than the bore of the cylinder, so that a scavenging action by intake gases takes place on opposite sides of said middle transverse plane in the form of transversely directed equicurrents on opposite sides of said middle transverse plane.

5. An internal combustion engine as claimed in claim 4, in which said intake transfer passages are at least four in number and are arranged diagonally pair-Wise so that the intake gases converge toward said one end of said diametral line.

References Cited by the Examiner UNITED STATES PATENTS 898,913 9/1908 Nelson 123--51 1,080,123 12/1913 Pratt 123-74 1,607,431 11/1926 Brice 123-74 1,662,740 3/ 1928 Dennison 123-51 1,789,190 1/1931 -Noble 123-74 1,890,794 12/1932 Penning 123-51 2,067,049 1/ 1937 Goldberg 123-51 2,112,829 3/193'8 Colburn 123-51 2,134,811 11/19'38 Church 123-51 2,647,498 8/1953 Hickey 123-51 FOREIGN PATENTS 65,004 5 1914 Austria.

531,009 12/1940 Great Britain.

558,115 `12/ 1943 Great Britain.

779,631 7 /1957 `Great Britain.

MARK NEWMAN, Primlwry Examiner.

W. BURNS, Assistant Examiner, 

1. AN OVERSQUARE INTERNAL COMBUSTION ENGINE COMPRISING AT LEAST A GROUP OF CYLINDERS MADE UP OF TWO CYLINDERS HAVING A LARGE DIAMETER BORE AND A MIDDLE TRANSVERSE PLANE, THE AXES OF SAID CYLINDERS BEING ARRANGED IN A SINGLE PLANE, A CRANKSHAFT HAVING TWO CRANKPINS AND EXTENDING NORMALLY TO THE PLANE CONTAINING THE AXES OF THE TWO CYLINDERS AND BETWEEN SAID CYLINDERS, A FIRST AND A SECOND RECIPROCATING PISTON MOUNTED IN OPPOSITION IN EACH CYLINDER FOR SYNCHRONOUSLY MOVING IN OPPOSITE DIRECTIONS, A ROCKER CONNECTED TO EACH PISTON, A ROLLER SECTOR COOPERATING WITH SAID ROCKER AND HAVING AN OUTER DIAMETER AND AN INNER DIAMETER, A PLATE MEMBER PROVIDED ON SAID PISTON, SAID OUTER DIAMETER OF SAID SECTOR ROLLING ON SAID PLATE MEMBER, WHILE SAID INNER DIAMETER IS JOURNALLED ON SAID ROCKER, A BEARING SEMICIRCLE PROVIDED IN SAID ROCKER, A PIN CARRIED BY SAID PISTON, SAID PIN BEING LATERALLY SLIDABLE ON SAID BEARING SEMI-CIRCLE, A PITMAN DIRECTLY CONNECTING THE FIRST PISTON ROCKER OF ONE CYLINDER TO THE DIAGONALLY OPPOSED SECOND PISTON ROCKER OF THE OTHER CYLINDER, MEANS ON SAID PITMAN FOR ENGAGING ONE CRANKPIN OF SAID CRANKSHAFT, INTAKE MEANS PROVIDED IN EACH CYLINDER NEAR ONE END OF A DIAMETER CONTAINED IN SAID MIDDLE TRANSVERSE PLANE OF SAID CYLINDER, AND EXHAUST MEANS PROVIDED IN SAID CYLINDER NEAR THE OTHER END OF SAID DIAMETER, SO AS TO ENSURE WITHIN SAID CYLINDER A SCAVENGING ACTION BY TRANSVERSELY DIRECTED EQUICURRENTS ABOUT SAID MIDDLE PLANE. 